Image Compositing Apparatus, Image Compositing Method, Image Compositing Program, and Recording Medium

1. An image compositing device configured to generate a composite image using a first image and a second image having different exposure conditions, the image compositing device comprising: an input unit configured to input the first image and the second image; a likelihood calculating unit configured to calculate a subject motion likelihood at each pixel based on a difference between the first image and the second image before estimating an exposure transform function for conforming the exposure conditions of the first image and the second image to each other; an exposure estimating unit configured to estimate the exposure transform function based on the subject motion likelihood; and a compositing unit configured to composite the first image and the second image by using the exposure transform function.

2. The image compositing device according to claim 1 , wherein the likelihood calculating unit is further configured to normalize pixel values of the first image and the second image, and to calculate the subject motion likelihood at each pixel based on a difference between the normalized first images and the normalized second images.

3. An image compositing device configured to generate a composite image using a first image and a second image having different exposure conditions, the image compositing device comprising: an input unit configured to input the first image and the second image; a likelihood calculating unit configured to calculate a subject motion likelihood at each pixel based on a difference between the first image and the second image; a compositing unit configured to composite the first image and the second image by using the exposure transform function, wherein the likelihood calculating unit is further configured to use a plurality of first processed images obtained by respectively intergrading resolutions of the first image and a plurality of second processed images obtained by respectively intergrading resolutions of the second image for calculating a difference of each pixel for each resolution, and to calculate the subject motion likelihood at each pixel by weighting a difference obtained for each resolution.

4. The image compositing device according to claim 3 , wherein the likelihood calculating unit is further configured to weight the difference obtained for each resolution based on a reliability of the difference between the first image and the second image and based on an image size or a resolution of the first processed image or the second processed image.

5. The image compositing device according to claim 1 , wherein the exposure estimating unit is further configured to select a sampling point for deriving the exposure transform function based on the subject motion likelihood at each pixel.

6. The image compositing device according to claim 1 , wherein the exposure estimating unit is further configured to determine a weight of a sampling point for deriving the exposure transform function based on the subject motion likelihood at each pixel.

7. The image compositing device according to claim 6 , wherein determination is made by the exposure estimating unit so as to make the weight of the sampling point for deriving the exposure transform function smaller as the subject motion likelihood at each pixel becomes higher.

8. The image compositing device according to claim 1 , wherein the compositing unit is further configured to calculate a subject motion likelihood at each pixel based on a difference between the first image and the second image, and composites the first image and the second image by using the subject motion likelihood and the exposure transform function.

9. The image compositing device according to claim 1 , wherein the compositing unit is further configured to generate a luminance base mask representing a composition ratio of pixel values of the first image and the second image based on a magnitude of an original luminance value of the first image or the second image, generate a subject blur mask representing a composition ratio of pixel values of the first image and the second image based on the difference between the first image and the second image, and combine the luminance base mask and the subject blur mask to generate a compositing mask for compositing pixel values of the first image and the second image.

10. The image compositing device according to claim 9 , wherein the compositing unit is further configured to calculate a subject motion likelihood at each pixel based on a difference between the first image and the second image, and generate the subject blur mask based on the subject motion likelihood.

11. The image compositing device according to claim 10 , wherein the compositing unit is further configured to use a plurality of first processed images obtained by respectively intergrading resolutions of the first image and a plurality of second processed images obtained by respectively intergrading resolutions of the second image for calculating a difference of each pixel for each resolution, calculate the subject motion likelihood at each pixel by weighting the difference obtained for each resolution, and generate the subject blur mask based on the subject motion likelihood.

12. The image compositing device according to claim 11 , wherein the compositing unit is further configured to detect regions in which pixels with a subject motion likelihood being equal to or lower than a predetermined threshold are adjacent to each other, to attach an identification label to each region, and to generate the subject blur mask for each region.

13. The image compositing device according to claim 9 , wherein the compositing unit is further configured to generate, as the subject blur mask, a first mask that forces a pixel value with a lower luminance value to be selected from among the first image and the second image or a second mask that forces a pixel value with a higher luminance value to be selected from among the first image and the second image.

14. The image compositing device according to claim 13 , wherein the compositing unit is further configured to generate the compositing mask by multiplying the luminance base mask with an inverted mask of the first mask or by adding the second mask to the luminance base mask.

15. The image compositing device according to claim 1 , further comprising a motion information acquiring unit configured to acquire motion information of a pixel between the first image and the second image, wherein the likelihood calculating unit is further configured to correct the first image and the second image based on the motion information, and to calculate the subject motion likelihood at each pixel using the corrected first and second images.

16. The image compositing device according to claim 1 , wherein the first image comprises an image being a composite of images with different exposure conditions.

17. An image compositing method for generating a composite image by using a first image and a second image having different exposure conditions, the image compositing method comprising: inputting the first image and the second image; calculating a subject motion likelihood at each pixel based on a difference between the first image and the second image before estimating an exposure transform function for conforming the exposure conditions of the first image and the second image to each other; estimating the exposure transform function based on the subject motion likelihood; and compositing the first image and the second image by using the exposure transform function.

18. A recording medium on which is recorded an image compositing program that causes a computer to operate so as to generate a composite image by using a first image and a second image having different exposure conditions, wherein the image compositing program recorded on the recording medium causes the computer to operate as: an input unit that inputs the first image and the second image; a likelihood calculating unit that calculates a subject motion likelihood at each pixel based on a difference between the first image and the second image before estimating an exposure transform function for conforming the exposure conditions of the first image and the second image to each other; an exposure estimating unit that estimates the exposure transform function based on the subject motion likelihood; and a compositing unit that composites the first image and the second image by using the exposure transform function.

19. An image compositing method for generating a composite image by using a first image and a second image having different exposure conditions, the image compositing method comprising: inputting the first image and the second image; calculating a subject motion likelihood at each pixel based on a difference between the first image and the second image; compositing the first image and the second image by using the exposure transform function; and using a plurality of first processed images obtained by respectively intergrading resolutions of the first image and a plurality of second processed images obtained by respectively intergrading resolutions of the second image for calculating a difference of each pixel for each resolution; calculating the subject motion likelihood at each pixel by weighting a difference obtained for each resolution.